Fears are growing for the welfare of Richard Ratcliffe, the husband of the detained Iranian-British dual national Nazanin Zaghari-Ratcliffe, who is on the 17th day of his hunger strike outside the Foreign Office. Some of his allies are urging him to stop, saying they are concerned he may damage himself permanently. Ratcliffe is also aware of his responsibility to look after his seven-year-old daughter, Gabriella. But after five and a half years of no tangible progress, and most campaigning avenues exhausted, Ratcliffe, who is spending his nights outside the Foreign Office in a tent, does not yet want to back down. Admitting he felt weaker, he said: “I’m definitely looking rougher and feeling rougher. I don’t feel hungry but I do feel the cold more. It’s a short-term tactic. You can’t take it too long or you end up in a coma.” Under one plan, he will end the hunger strike when the Iranian delegation leave Cop26 in Glasgow later this week. He ended a previous hunger strike outside the Iranian embassy in London after 15 days, but it took place in the summer. The Labour leader, Keir Starmer, and his deputy, Angela Rayner, visited Ratcliffe outside the Foreign Office on Tuesday, joining a steady stream of well-wishers, including MPs from all parties that are giving solidarity to his campaign. The former foreign secretary Dominic Raab said the government was doing everything it could to secure Zaghari-Ratcliffe’s release. Asked on Sky News whether he believed payment of a £400m debt owed by the UK to Iran over a weapons deal would bring Zaghari Ractliffe and other dual nationals home, Raab said: “It is not clear to me at all and I do not think there should be a quid pro quo.” A former Conservative minister told the Guardian: “As I understand it, the prime minister, the foreign secretary and the defence secretary all want to pay the debt, so unless they are not telling the truth, what under the British constitution is holding them back?” He said mechanisms had been agreed with the Iranians for the money to be paid through humanitarian channels, and commitments had been given, valuable or otherwise, that the money would not be transferred to the Islamic Revolutionary Guards Corps. Some of Ratcliffe’s friends fear he is becoming more inflexible, and unless the Foreign Office comes up with some tangible sign of progress, he could continue to a point of self-damage. It is generally accepted that after two weeks, dizziness, difficulties standing, low heart rate and chills start to intensify. Three weeks can lead to long-term complications. The foreign secretary, Liz Truss, on a trip to the far east this week, spoke on the phone to the Iranian foreign minister, Hossein Amir-Abdollahian, on Monday in what the latter described as “a useful call”. He reiterated his demand that the UK urgently repay the “long overdue” £400m debt to Iran, outstanding since the 1970s. Truss has been privately advised by at least two former Conservative Foreign Office ministers that Zaghari-Ratcliffe, who is out of prison on furlough but due to serve another year’s sentence, will not be returned to the UK unless the debt is repaid. She has been detained since April 2016. In a meeting with Ratcliffe shortly after he began his hunger strike, Truss was not able to give him any news on payment of the debt, leaving him frustrated at the secrecy and apparent lack of progress. News of the call between the foreign ministers was released by the Iranians. The deputy foreign minister, Ali Bagheri Kani, will visit London, Paris and Germany later this week as part of preparations for resuming the long-delayed talks in Vienna on 29 November over the US’s return to the nuclear deal. The Foreign Office has assured families of British nationals that officials and ministers will raise their plight with Bagheri. It said it would use Kani’s visit “to press firmly for the immediate release of our unfairly detained British nationals”. At a weekly press conference in Tehran on Monday, the Iranian foreign ministry spokesperson Saeed Khatibzadeh was asked by Iranian reporters about Ratcliffe’s hunger strike. He said: “Humanitarian issues must be pursued within a humanitarian context. We are sorry that some people in the UK and other countries have made humanitarian issues hostage to other political issues.”